NPs have found several applications due to their high specific surface area and unique optical, electrical and magnetic properties in fields such as medical diagnostics, drug delivery, foods, energy and catalysis, combinatorial libraries, semiconductors and electronics.1-6 A key challenge in phase-transfer of NPs involves the prevention of drastic alterations to the functional properties of NPs while in aqueous phase. A well documented example is the degradation in optical properties of CdSe quantum dots (QD) in water, brought about by water-induced fluorescence quenching. Methodologies to prevent QD surfaces from coming in contact with water include the growth of physical barriers such as a shell (core-shell quantum dots) or the use of surfactant and polymeric systems to disperse and protect the NPs from interactions with water.7,8 
Previous groups have employed microemulsion/emulsion/surfactant routes to phase-transfer NPs to water.9-12 Fan et al. (2005) discuss a process to phase-transfer NPs dissolved in chloroform by formulating an oil in water microemulsion with chloroform as oil and cetyl trimethylammonium bromide (CTAB) as surfactant, wherein chloroform is evaporated by heating the microemulsion. This process gives aqueous dispersions of NPs with high stability, but results in drastic lowering in functional properties of NPs, specifically luminescence.10 
Dubertret et al. (2002) report successful dispersion of single quantum dots in water using twin-tailed surfactants such as 1,4-Bis(2-ethylhexyl) sodium sulfosuccinate (Aerosol OT or AOT).11 In their proposed route, quantum dots were dissolved in chloroform to which AOT was added, and the chloroform was evaporated to leave behind a residue. The residue was then heated at 80° C. after which 1 mL of water was added to give a stable clear dispersion of quantum dots in water. When the procedure discussed above was repeated with addition of salt (unspecified composition) in lieu of pure water, the resulting quantum dot suspensions were reported to be unstable.11 Thus, Dubertret teaches away from using salt to improve phase transfer.
Li et al. (2007) report phase-transfer of CdSe/ZnS core-shell quantum dots from chloroform to water. CdSe/ZnS core-shell quantum dots were solubilized in chloroform upon which the mixture was transferred to a solution of Gemini 12-4-12 surfactant that resulted in the formation of oil-in-water microemulsion. The core-shell quantum dots were phase-transferred to water by evaporating chloroform at 50° C. for 30 minutes. Photoluminescence studies revealed an increase in intensity of core-shell quantum dots in aqueous phase over those in chloroform and the phase transferred NP dispersion was found to be stable. The authors also mention in the paper that the NP dispersions were stable even after two months, in terms of photoluminescence intensities. No photoluminescence intensities values measured after 2 months were published in the paper, however, and it is important to note that the reported luminescence values were for a CdSe—ZnS core-shell structure,12 not a naked QD.
Schematic 1, displayed in FIG. 20, summarizes current methods to phase-transfer NPs, wherein NPs present in oil are added to water that contains a dispersing/stabilizing agent (surfactant). Surfactants have “oil-loving” (hydrophobic) and “water-loving” (hydrophilic) groups in its chemical structure and exist as structures called “micelles” in water. The hydrophilic ends of the micellar structure face water, whereas the hydrophobic groups are shielded from water and are located in the interior of the micelle.13 When oil is added to water containing surfactant micelles, the surfactant molecules partition to the interface of oil and water so as to disperse oil in water. These dispersions are then heated to evaporate or “boil-off” the oil. Consequently, NPs are contained within the hydrophobic part of the micelle and the hydrophilic portion disperses them in water.
However, what is needed in the art are better methods to phase-transfer NPs to water without disturbing key properties of the nanoparticles.